Multiplexing two separate optical links with the same wavelength using asymmetric combining and splitting

ABSTRACT

An optical communications system includes an optical transmitter and an optical receiver optically coupled to an optical combiner/splitter, the combiner/splitter coupled to optical media; and, another optical transmitter and another optical receiver optically coupled to another optical combiner/splitter, the another combiner/splitter remotely coupled to the optical media; wherein the optical transmitter and the another optical transmitter are configured to transmit optical signals at substantially the same wavelength.

PRIORITY APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/962,279 filed on Dec. 8, 2015, which claims the benefit of priorityto U.S. Provisional Application No. 62/090,658, filed on Dec. 11, 2014,the content of both are relied upon and incorporated herein by referencein their entireties.

BACKGROUND Technical Field

Embodiments disclosed herein relates to communications within an opticalnetwork, and in particular, to methods and apparatus for multiplexingdata signals.

Description of the Related Art

With the exponential growth in communications, there is a continuingdemand for increased capacity. Generally, expanding capacity of fiberoptic systems has been achieved by installing more cables; increasingsystem bitrate; and by wavelength division multiplexing.

Wavelength division multiplexing (WDM) uses existing electronics andfibers, and simply shares fibers by transmitting different channels atdifferent wavelengths. Generally, a wavelength division multiplexing(WDM) system uses a multiplexer at the transmitter to join opticalsignals together and a demultiplexer at the receiver to split themapart. Most wavelength division multiplexing (WDM) systems operate onsingle-mode fiber optical cables, which have a core diameter of 9 μm.One type of wavelength division multiplexing (WDM) system is referred toas a “coarse wavelength division multiplexing (CWDM)” system. Generally,coarse wavelength division multiplexing (CWDM) systems provide up toeight (8) or nine (9) communications channels. Coarse wavelengthdivision multiplexing (CWDM) uses increased channel spacing (spacingbetween wavelength groupings) to permit use of less sophisticatedtransceiver equipment.

Unfortunately, with the ever increasing demand for bandwidth, this isnot adequate. As cable installation is a laborious and costly process,it is desirable to increase signal transmission using existinginfrastructure. Thus, what are needed are methods and apparatus toincrease signal transmission over existing implementations of fiberoptics.

SUMMARY

In one embodiment, an optical communications system is provided. Thesystem includes an optical transmitter and an optical receiver opticallycoupled to an optical combiner/splitter, the combiner/splitter coupledto optical media; and, another optical transmitter and another opticalreceiver optically coupled to another optical combiner/splitter, theanother combiner / splitter remotely coupled to the optical media;wherein the optical transmitter and the another optical transmitter areconfigured to transmit optical signals at substantially the samewavelength.

At least one of the combiner/splitter and the another combiner/splittermay include an asymmetric combiner/splitter. The asymmetriccombiner/splitter may include a high transmittance ratio, T_(R), and alow transmittance ratio, T_(R). The high transmittance ratio, T_(R), andthe low transmittance ratio, T_(R), may have a combination of ratiosthat is one of 95/5, 90/10, 85/15, 80/20, 75/25, 70/30 and a ratiotherebetween. At least one of the optical transmitter and the anotheroptical transmitter is substantially insensitive to optical interferencereceived at the operational wavelength. The optical media may include asingle-mode optical fiber. A low transmittance ratio, T_(R), may beassociated with each of the optical transmitters. A high transmittanceratio, T_(R), may be associated with each of the optical receivers.

In another embodiment, a method for providing an optical networkconfigured for bi-directional communication using optical signals isprovided. The method includes: selecting a first operator that includesan optical transmitter and an optical receiver optically coupled to anasymmetric optical combiner/splitter, the combiner/splitter and couplingthe first operator to a first end of optical media; and, selectinganother operator that includes another optical transmitter and anotheroptical receiver optically coupled to another asymmetric opticalcombiner/splitter, the another operator remotely coupled to the opticalmedia.

The method may further call for selecting the another opticaltransmitter for operation at substantially the same wavelength as theoptical transmitter. The method may further call for associating a lowtransmittance ratio, T_(R), of each of the combiner/splitters with arespective one of the optical transmitters. The method may further callfor associating a high transmittance ratio, T_(R), of each of thecombiner/splitters with a respective one of the optical receivers. Themethod may further call for selecting a Fabry-Perot laser as at leastone of the optical transmitters.

In another embodiment, an optical network is provided. The networkincludes an optical fiber; a first plurality of optical transmitters andreceivers at a first end of the optical fiber, each optical transmitterand receiver configured to transmit and receive an optical link; a firstoptical line terminal at a first end of the optical fiber, the firstoptical line terminal configured to combine or split two optical linksof the same wavelength on the same media; a second plurality of opticaltransmitters and receivers at a second end of the optical link, eachoptical transmitter and receiver configured to transmit and receive anoptical link; a second optical line terminal at a second end of theoptical fiber, the second optical line terminal configured to combine orsplit two optical links of the same wavelength on the same media; afirst course wide division multiplex (CWDM) terminal, the first CWDMconnected at a first end to the first plurality of optical transmittersand receivers and the first optical line terminal and at a second end tothe optical fiber, the first CWDM configured to route optical linksbi-directionally between the first plurality of optical transmitters andreceivers and the first optical line terminal and the second pluralityof optical transmitters and receivers; a second course wide divisionmultiplex (CWDM) terminal, the second CWDM connected at a first end tothe second plurality of optical transmitters and receivers and thesecond optical line terminal and at a second end to the optical fiber,the second CWDM configured to route optical links bi-directionallybetween the second plurality of optical transmitters and receivers andthe second optical line terminal and the first plurality of opticaltransmitters and receivers.

Each of the first optical line terminal and the second optical lineterminal may exhibit a high transmittance ratio, T_(R), and a lowtransmittance ratio. The high transmittance ratio, T_(R), and the lowtransmittance ratio, T_(R), may include a combination of ratios that isone of 95/5, 90/10, 85/15, 80/20, 75/25, 70/30 and a ratio therebetween.A combination of the high transmittance ratio, T_(R), and the lowtransmittance ratio, T_(R), may be about 90/10. At least one of thefirst plurality of optical transmitters and at least one of the secondplurality of optical transmitters may be substantially insensitive tooptical interference received at the operational wavelength. The opticalfiber may be a single-mode optical fiber. The low transmittance ratio,T_(R), may be associated with each of the optical transmitters. The hightransmittance ratio, T_(R), may be associated with each of the opticalreceivers.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from the description or recognized by practicing theembodiments as described in the written description and claims hereof,as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary, and areintended to provide an overview or framework to understand the natureand character of the claims.

The accompanying drawings are included to provide a furtherunderstanding, and are incorporated in and constitute a part of thisspecification. The drawings illustrate one or more embodiment(s), andtogether with the description serve to explain principles and operationof the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an schematic diagram depicting elements of a communicationssystem for same wavelength signaling;

FIG. 2 is schematic diagram depicting elements of the communicationssystem of FIG. 1 integrated into a coarse wavelength divisionmultiplexing (CWDM) system; and

FIG. 3 is a flow chart depicting an exemplary method according to thisdisclosure.

DETAILED DESCRIPTION

Disclosed herein are techniques for communicating data with a singleband of wavelengths using two separate optical links over a singlefiber. The techniques for “same wavelength multiplexing” make use ofasymmetrical combining and splitting of the single band of wavelengths.Advantageously, the techniques provide for substantially increasedcommunication capacity over an existing fiber optic system. Prior todiscussing the invention in detail, some aspects are introduced.

As discussed herein, the term “wavelength” generally relates to a groupof wavelengths used for communicating an optical signal. That is, it isnot required that the optical signal be communicated at precisely onewavelength, but that the optical signal is communicated in a group ofwavelengths that may be functionally considered as being associated withthe optical signal. More specifically, each “wavelength” may actuallyinclude a distribution wavelengths. The distribution may be centeredaround the identified wavelength, or the identified wavelength maysimply be within the grouping of wavelengths.

As discussed herein, the term “channel,” “optical link,” and othersimilar terms generally refer to a single data stream that iscommunicated over communications equipment.

Referring now to FIG. 1, there are shown aspects of an exemplaryembodiment of a communications system 100. The communication system 100provides for the delivery of two (2) communications channels usingcommon communications equipment.

In this embodiment, a first operator 10 communicates with a secondoperator 20 over optical media 110. Exemplary optical media 110 includesa single mode optical fiber. The first operator 10 includes equipmentthat is substantially similar or identical to the equipment maintainedby the second operator 20. Alternatively, the equipment of the firstoperator 10 and second operator 20 may be different. Of course, each ofthe first operator 10 and the second operator 20 may maintainsubstantially more equipment than shown here. That is, the equipmentshown and described is limited to that which provides for communicationsaccording to the teachings herein. Additional equipment and componentsmay be included as desired, but will not be discussed further herein.

More specifically, the first operator 10 includes an optical receiver122 for a first channel (RX1) and an optical transmitter 124 for asecond channel (TX2). The optical receiver 122 and the opticaltransmitter 124 are optically coupled to a combiner/splitter 120. Theoptical receiver 122 is optically coupled to the combiner/splitter 120at receiver port 114. The optical transmitter 124 is optically coupledto the combiner/splitter 120 at transmitter port 116. Thecombiner/splitter 120 is optically coupled to the optical media 110 atfiber port 112.

Similarly, the second operator 20 includes an optical receiver 126 forthe second channel (RX2) and an optical transmitter 102 for the firstchannel (TX1). The optical receiver 126 and the optical transmitter 102are optically coupled to a combiner/splitter 118. The optical receiver126 is optically coupled to the combiner/splitter 118 at receiver port106. The optical transmitter 102 is optically coupled to thecombiner/splitter 120 at transmitter port 104. The combiner/splitter 118is optically coupled to the optical media 110 at fiber port 108.

It should be noted that the use of “RX” and “TX” nomenclature herein (inparticular, with regards to FIGS. 1 and 2) generally refer to aspects ofcommunications for a given channel. That is, RX refers to receiving asignal, while TX refers to transmitting a signal. The following Arabicnumber refers to the specific channel (channel 1, channel 2, and so on).

Each of the combiner/splitters 118, 120 is asymmetric. For example, inthe embodiment shown, for the first operator 10, the combiner/splitter120 has a transmittance ratio, T_(R), of x0.9 from the fiber port 112 tothe receiver port 114. The combiner/splitter 120 has a transmittanceratio, T_(R), of x0.1 from the transmitter port 116 to the fiber port112. In this exemplary embodiment, the isolation level between thetransmitter port 116 and the receiver port 114 is about 60 dB. In theexemplary embodiment, the transmittance ratios, T_(R), provide adequateattenuation between the optical transmitters 124, 102 while transmittingadequate energy to respective optical receiver 126, 122.

By appropriately configuring the communication system 100, it ispossible to provide for communications where a first signal does notsubstantially interfere with a second signal. For example, consider afirst signal generated for the first channel (TX1). The first signal isgenerated by the optical transmitter 102. The first signal generated bythe optical transmitter 102 will be attenuated when transmitted from therespective transmit port 104 of the combiner/splitter 118 to the fiberport 108. When transmitted through the combiner/splitter 118, the firstsignal will be attenuated by a low transmittance ratio, T_(R), (in thiscase, T_(R)=0.1). When the first signal is received by the opposingcombiner/splitter 120, the first signal will be split. A first portionof the first signal will be transmitted from fiber port 112 to thereceiver port 114 and on to optical receiver 122, and will be furtherattenuated by a second, higher, transmittance ratio, T_(R), (in thiscase, T_(R)=0.9). Accordingly, the optical energy transmitted by theoptical transmitter 102 and reaching the respective optical receiver 122will be: Energy*(0.1*0.9), or 0.09*Energy.

Similarly, a second portion of the first signal transmitted from fiberport 112 to the receiver port 116 and on to optical transmitter 124 willbe further attenuated by a second, lower, transmittance ratio, T_(R),(in this case, T_(R)=0.1). Accordingly, optical energy transmitted bythe optical transmitter 102 and received at the opposing opticaltransmitter 124 (for TX2) will be: Energy*(0.1*0.1), or 0.01*Energy.

In general, each of the combiner/splitters 118, 120 includes anasymmetric set of transmittance ratios, T_(R). The asymmetric set oftransmittance ratios, T_(R), includes a low coefficient and a highcoefficient.

In the same example, a second signal is generated for the second channel(TX2) by the opposing optical transmitter 124. The second signalgenerated by the optical transmitter 124 will be attenuated by a lowtransmittance ratio, T_(R), (in this case, T_(R)=0.1) when transmittedfrom the respective transmit port 116 of the combiner/splitter 120 tothe fiber port 112. When the second signal is received by the opposingcombiner/splitter 118, the second signal will be split. A first portionof the second signal transmitted from fiber port 108 to the receiverport 106 and on to optical receiver 126 will be further attenuated by asecond, higher, transmittance ratio, T_(R), (in this case, T_(R)=0.9).Accordingly, the optical energy transmitted by the optical transmitterand reaching the respective optical receiver 126 will be:Energy*(0.1*0.9), or 0.09*Energy.

Similarly, a second portion of the second signal transmitted from fiberport 108 to the receiver port 104 and on to optical transmitter 102 willbe further attenuated by a second, lower, transmittance ratio, T_(R),(in this case, T_(R)=0.1). Accordingly, optical energy transmitted bythe optical transmitter 124 and received at the opposing opticaltransmitter 102 (for TX1) will be: Energy*(0.1*0.1), or 0.01*Energy.

In other words, by appropriately configuring the pair ofcombiners/splitters 118, 120, a respective optical receiver 122 willreceive adequate optical energy to provide for signal discrimination. Atthe same time, with an appropriate type of optical transmitter, theopposing optical transmitter 124 does not receive signal energy that issubstantial enough to cause interference with optical transmission.

Exemplary components for use as the optical transmitter 102, 124 includeFabry Perot lasers.

In view of the above, bi-directional communications over a single fiberwith opposing optical signals that are centered around a singlewavelength are achievable.

Selection of appropriate combiner/splitter components may includeconsideration of length of the optical media 110 (that is, a degree ofattenuation within the optical media 110), power of the respectiveoptical transmitters, types of optical transmitters, sensitivity ofoptical receivers, cost, availability and other such factors.

FIG. 2 illustrates aspects of an exemplary embodiment of an opticalnetwork 200 that makes use of the teachings herein. Optical network 200includes an optical fiber 210; a first plurality of optical transmittersand receivers (TX1, RX2, TX3, RX4, TX5, RX6, TX7, RX8, RX9, TX10) at afirst end of the optical fiber 210, each optical transmitter andreceiver is configured to transmit and receive an optical link(respectively). A second plurality of optical transmitters and receivers(RX1, TX2, RX3, TX4, RX5, TX6, RX7, TX8, TX9, RX10) are provided at asecond end of the optical fiber 210, each optical transmitter andreceiver configured to transmit and receive an optical link(respectively).

Optical network 200 further includes a first course wide divisionmultiplex (CWDM) terminal 202. The first CWDM terminal 202 is connectedat a first end to the first plurality of optical transmitters andreceivers. The first CWDM terminal 202 is configured to route opticallinks bi-directionally between the first plurality of opticaltransmitters and receivers and the optical fiber 210. The second CWDMterminal 204 is connected to the second plurality of opticaltransmitters and receivers and the optical fiber 210. The second CWDMterminal 204 is configured to route optical links bi-directionallybetween the second plurality of optical transmitters and receivers andthe optical fiber 210.

In the exemplary embodiment, the optical network 200 is configured tooperate with ten communications channels (TX/RX1, TX/RX2, . . .TX/RX10). The optical network 200 makes use of nine separate wavelengths(λ1, λ2, . . . λ9). Communications channels TX/RX9 and TX/RX10 make useof a single wavelength, λ9.

In this exemplary embodiment, the first coarse wavelength divisionmultiplexing (CWDM) terminal 202 is configured with equipment as may beknown in the art for generating, transmitting and receiving opticalsignals in an optical communications system. Similarly, the secondcoarse wavelength division multiplexing (CWDM) terminal 204 isconfigured with equipment as may be known in the art for generating,transmitting and receiving optical signals in an optical communicationssystem.

The first coarse wavelength division multiplexing (CWDM) terminal 202 isalso configured with combiner/splitter 206 which is configured toprovide for communicating data with a single band of wavelengths (λ9)using two separate optical links (TX/RX9 and TX/RX10) over optical fiber210. The second coarse wavelength division multiplexing (CWDM) terminal204 is also configured with combiner/splitter 208 which is configured toprovide for communicating data with a single band of wavelengths (λ9)using two separate optical links (TX/RX9 and TX/RX10) over the opticalfiber 210.

FIG. 3 depicts an exemplary method for assembling an optical networkaccording to the teachings herein. In the exemplary method for opticalnetwork assembly 300, a first step 301 calls for selecting an assemblythat includes an optical transmitter, an optical receiver and acombiner/splitter. In a second step 302, the assembly is coupled tooptical media, such as an optical fiber. The first step 301 and thesecond step 302 may be repeated as many times as needed to complete theoptical network.

Having set forth exemplary embodiments, some additional aspects are nowintroduced.

The teachings herein may be applied in any type of optical communicationsystem and/or architecture deemed appropriate. For example, in someother embodiments of a coarse wavelength division multiplexing (CWDM)system, at least some of the other wavelengths (λ1, λ2, . . . λ8) areused for “same wavelength multiplexing” techniques as provided for withregard to FIG. 5.

The optical transmitter may include any device deemed appropriate.Generally, optical transmitters are selected for insensitivity to lowlevels of optical interference at the operational wavelength of theoptical transmitter. That is, in general, each optical transmitter issubstantially insensitive to wavelengths received from the opposingoptical transmitter (as a result of attenuation by the twocombiner/splitter elements in combination with the properties of theoptical transmitter). In some embodiments, the optical transmitterincludes a Fabry Perot laser. In some other embodiments, the opticaltransmitter includes a discrete coaxial packaged laser, a small formpluggable (SFP) transceivers, a small form pluggable plus (SFP+)transceivers (if using FP) and other such devices.

The optical receiver may include any device deemed appropriate.Generally, optical receivers are selected for sensitivity to low levelsof optical signals at the operational wavelength. In some embodiments,the optical receiver includes any one of a discrete coaxial packagedphotodiode, a SFP transceivers, a SFP+ transceivers any other similardevice.

Wavelengths may be centered around any wavelength deemed appropriate.For example, wavelengths may be centered about groupings used byconventional optical systems. More specifically, wavelengths selectedfor use in a communications channel may be centered about any one of1270, 1310, 1350, 1400, 1480, 1550, and 1630 nm.

Optical combiners/splitters may employ any distribution of transmittanceratios, T_(R), deemed appropriate. For example, the transmittanceratios, T_(R), may include high/low combinations such as: 95/5, 90/10,85/15, 80/20, 75/25, 70/30 and ratios there between.

Other optical devices may be included. For example, a variety of opticalcouplings and associated components may be included.

The combiner/splitter units selected may operate on any principle deemedappropriate. For example, in some embodiments, the combiner/splitterusing polarizing technology. Attenuators, absorbers, reflectors,birefringent elements and other such components may be included withinthe combiner/splitter (or elsewhere) within the communications system.

The optical media may include a continuous fiber, an optical network, orany other optical system deemed appropriate. It is not required that theoptical media be a single, continuous fiber. For example, in someembodiments, at least another splitter may be incorporated. That is, insome embodiments, one combiner/splitter is coupled to one end of theoptical media, while an opposing combiner/splitter is coupled to anopposing end of the optical media. In some other embodiments, such aswhere intermediate couplings, other devices and/or multiple operatorsare used, one combiner/splitter is coupled to the optical media, whileanother combiner/splitter is remotely coupled to the optical media.

One set of wavelengths is substantially the same as another set ofwavelengths if systems using the wavelengths are functionally adequatein performance.

Various other components may be included and called upon for providingfor aspects of the teachings herein. Standards of performance are to bejudged by a system designer, manufacturer, user or other similarlyinterested party. The term “substantial” as used herein generallyrelates to adequacy of resulting system performance.

When introducing elements of the present invention or the embodiment(s)thereof, the articles “a,” “an,” and “the” are intended to mean thatthere are one or more of the elements. Similarly, the adjective“another,” when used to introduce an element, is intended to mean one ormore elements. The terms “including” and “having” are intended to beinclusive such that there may be additional elements other than thelisted elements.

Unless otherwise expressly stated, it is in no way intended that anymethod set forth herein be construed as requiring that its steps beperformed in a specific order. Accordingly, where a method claim doesnot actually recite an order to be followed by its steps or it is nototherwise specifically stated in the claims or descriptions that thesteps are to be limited to a specific order, it is no way intended thatany particular order be inferred.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the invention. Since modifications combinations,sub-combinations and variations of the disclosed embodimentsincorporating the spirit and substance of the invention may occur topersons skilled in the art, the invention should be construed to includeeverything within the scope of the appended claims and theirequivalents.

What is claimed is:
 1. A method for providing an optical networkconfigured for bi-directional communication using optical signals, themethod comprising: selecting a first operator comprising a first opticaltransmitter and a second optical receiver optically coupled to a firstasymmetric optical combiner/splitter, the combiner/splitter coupling thefirst operator to a first end of optical media; and selecting a secondoperator comprising a second optical transmitter and a second opticalreceiver optically coupled to a second asymmetric opticalcombiner/splitter, the second operator being remotely coupled to theoptical media.
 2. The method of claim 1, further comprising selectingthe second optical transmitter for operation at substantially the samewavelength as the first optical transmitter.
 3. The method of claim 2,further comprising associating a low transmittance ratio, T_(R), of eachof the asymmetric combiner/splitters with a respective one of theoptical transmitters.
 4. The method of claim 3, further comprisingassociating a high transmittance ratio, T_(R), of each of the asymmetriccombiner/splitters with a respective one of the optical receivers. 5.The method of claim 4, wherein the high transmittance ratio and the lowtransmittance ratio comprise a combination of ratios that is one of95/5, 90/10, 85/15, 80/20, 75/25, 70/30, and a ratio therebetween. 6.The method of claim 4, wherein the first optical transmitter issubstantially insensitive to optical interference received at anoperational wavelength of the optical network.
 7. The method of claim 6,wherein the second optical transmitter is substantially insensitive tooptical interference received at the operational wavelength of theoptical network.
 8. The method claim 5, further comprising selecting aFabry-Perot laser as at least one of the optical transmitters.
 9. Themethod of claim 4, wherein the high transmittance ratio and the lowtransmittance ratio comprise a combination of ratios that is about90/10.
 10. The method of claim 1, further comprising: associating a lowtransmittance ratio, T_(R), of each of the asymmetric combiner/splitterswith a respective one of the optical transmitters; and associating ahigh transmittance ratio, T_(R), of each of the asymmetriccombiner/splitters with a respective one of the optical receivers. 11.The method of claim 10, wherein: the first optical transmitter issubstantially insensitive to optical interference received at anoperational wavelength of the optical network; and the second opticaltransmitter is substantially insensitive to optical interferencereceived at the operational wavelength of the optical network.
 12. Themethod of claim 10, wherein the high transmittance ratio and the lowtransmittance ratio comprise a combination of ratios that is about90/10.
 13. The method of claim 10, wherein the high transmittance ratioand the low transmittance ratio comprise a combination of ratios that isone of 95/5, 90/10, 85/15, 80/20, 75/25, 70/30, and a ratiotherebetween.
 14. The method of claim 13, wherein the first opticaltransmitter is substantially insensitive to optical interferencereceived at an operational wavelength of the optical network.
 15. Themethod of claim 14, wherein the second optical transmitter issubstantially insensitive to optical interference received at anoperational wavelength of the optical network.